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Friday, August 26, 2016

The NAA VLF Station (NOT QRP!) and Brad's Receiver

NAA Towers -- Arlington Va. 1913

Brad WA8WDQ wrote to us about a VLF (24 kHz) his receiver project (see below).  This led to some Googling about the VLF station NAA.  Wow, there is some important radio history associated with that call sign.   The station's original location was just a few miles from I where I live now.  From Wikipedia  (https://en.wikipedia.org/wiki/VLF_Transmitter_Cutler):

The station began operations in 1913 as a radio telegraphy station call sign NAA in Arlington, Virginia, at a facility next to Fort Myer. Although its broadcasts occasionally included band concerts and speeches, it was most famous for its nightly time signals. The three towers known then as "The Three Sisters" stood 600 feet, 450 feet and 200 feet (183, 137, and 61 m) above the ground. The site was referred to as "Radio", Virginia. The towers were the second largest man-made structure in the world behind only the Eiffel Tower. The word "Radio" was first used instead of "Wireless," in the name of this Naval Communications facility. The First Trans-Atlantic voice communication was made between this station and the Eiffel Tower in 1915. The Nation set its clocks by the signal and listened for its broadcast weather reports. The Towers were dismantled in 1941 as a menace to aircraft approaching the new Washington National Airport. The towers stand today at United States Naval Academy in Maryland, on the edge of the Chesapeake Bay. 

Be sure to read about the de-icing system for the antenna.  It uses more power than the actual transmitter!

From Brad:

Bill, Pete,
Here's the current status of the 24 KHz NAA SID receiver.  All the major sub-assemblies are mounted in the chassis and power is hooked up.  For convenience, I've been using the PowerWerx USBbuddy switching DC-DC converter to supply +5V power to the Raspberry Pi from the +12V input.  I've found them extremely RF quiet, clean and stable; capable of supplying 3A though this project will only need about 1.5A @ +5V.  At this point, I'm just waiting for Adafruit to send the A/D chip I'll wire up to the Pi on that empty protoboard just under the meter.  Speaking of the meter, it's not really needed as the Pi records and broadcasts over Wi-Fi the received signal level.  However, I like my projects to have some sort of physical human interface so I added the signal level meter and an LED for SID event alarms :).

As previously mentioned, my bench test of the receiver using my signal generator was successful.  Once everything is wired, I'll do an actual on-air signal test receiving NAA.

Brad  WA8WDQ


Monday, August 22, 2016

Radio New Zealand Booming in on 7245 AM

The day is off to a good start here at SolderSmoke HQ, with Radio New Zealand booming in on my homebrew Mate for the Mighty Midget receiver.  I was listening from around 0900 to 1030 UTC on 7245 kHz. Once again we see that The Radio Gods favor homebrew receivers. Gray line propagation also played a role.  

Above we see a technician at work at RNZ in 1945.  More historic photos here:
http://www.pcc.govt.nz/About-Porirua/Porirua-s-heritage/Porirua-s-suburbs/Titahi-Bay/Historic-site--Radio-New-Zealand-Transmission-Station

Sunday, August 21, 2016

First Signals from the PA3GSV Mighty Midget Mate



Obviously the Radio Gods (Spirits in the Sky) approve of Jan's work.  How could they not?  I can now see why he took the trouble to cut that hole in the sewer pipe cap that forms the large wheel on his homebrew reduction drive.  But what are we going to see through that center hole Jan?  What will the frequency readout be like?  
----------------------
Hi  Bill,

Just finished the last stage of the Mighty Midget MK2.
There are first signals!
The first one I heard was a broadcast station, believe it or not, the song that was on was “Spirit in the Sky” ..
All stages were built, tested and as far as possible, adjusted separately.
It was built from back to front, so the RF amplifier was last.
I added an ECL82 for more audio, the first thought of only using an EL84 didn’t bring enough.
The triode of the ECL82 as a pre-amp, the pentode as final.
Furthermore ECF82’s were used instead of the 6U8, they’re more widely available over here.
The Miller coils are hard to come by, so the 300 uH coils are homebrew.
Also used a grid detector instead of the two germanium diodes.
The triode of V1 originally intended for audio was used for this.
Made the BFO adjustable as well, still remember the screwdriver sticking out of the coil on your side... 
 
Happily there was not much troubleshooting needed.
The 80m coil was only 5 kHz off, the 40m coil 300 kHz (to low in frequency), still have to fix that.
Initially the receiver worked reasonably well without adjusting, but C1 quit at some point.
After some investigation, the problem was a dirty wiper contact on the rotor.
An ultrasonic bath fixed the problem, so no looking out for a replacement there. (hope it stays that way)
 
After adjusting, sensitivity is around -114dBm (0,4 uV) / 10 dB S/N!  (with the FT241 crystals in place, and careful tuning of the controls)
Really not bad for this small receiver, Lew McCoy was right, it really is a Mighty Midget.
I wanted to make some video’s, but over here there’s a terrible S9 rattle from 160 to 15 meters.
Every now and then it appears out of nowhere, and disappears the same way.
As soon as it is gone, I’ll make some video’s.
I made one video though, just after completing the receiver.
 
 
Reception on CW and SSB sounds really well, but unfortunately didn’t record that.
The receiver is not finished yet.
Next to the 40m coil,  S-meter has to be tried, and there’s still some work on the cabinet and front panel.
 
More to follow.
   
73  Jan
PA3GSV

Wednesday, August 17, 2016

N7UN Talks About Summits on the Air (FDIM Interview by Bob Crane)

Bob Crane, our intrepid correspondent at the Dayton Hamvention talked to Guy N7UN (pictured above) about taking ham radio up to the mountaintops.  It was nice to hear Guy mention Wayne Burdick and Wes Hayward and WG0AT.    Thanks Bob!  Thanks Guy!

Listen here:

http://soldersmoke.com/N7UN.mp3

More on N7UN here:

http://www.n7un.com/


Designer: Douglas Bowman | Dimodifikasi oleh Abdul Munir Original Posting Rounders 3 Column